Oxidation step in electrolysis of aqueous hci

ABSTRACT

THE CURRENT INVENTION PERTAINS TO PROCESSES COMPRISING ELECTROLYZING HYDROCHLORIC ACID IN A DIAPHRAGM CELL HAVING AN ANOLYTE AND A CATHOLYTE TO PRODUCE CHLORINE. MORE PARTICULARLY, IT CONCERNS ADDING A SUBSTANTIALLY NON-FOAMING, WATER-SOLUBLE, IONIC, ORGANIC COMPOUND TO THE CATHOLYTE, AND DISPERSING AN OXIDIZING GAS THEREIN TO FORM SMALL BUBBLES AND OXIDIZE THE CATHOLYTE. THE ORGANIC ADDITIVE, WHICH INDUCES A SMALLER BUBBLE SIZE, EFFECTS A REDUCTION IN POWER CONSUMED BY THE DISPERSING MEANS AND INCREASES THE OXIDATION RATE OF METAL IONS IN THE CATHOLYTE.

United States Patent O ABSTRACT OF THE DISCLOSURE The current invention pertains to processes comprising electrolyzing hydrochloric acid in a diaphragm cell hav ing an anolyte and a catholyte to produce chlorine. More particularly, it'concernsadding a substantially non-foaming, water-soluble, ionic, organic compound to the catholyte, and dispersing an oxidizing gas therein to-forrn small bubbles and oxidize the catholyte. The organic additive,

which induces a smaller bubblesize, effects a reduction in power consumed by the dispersing means and increases the oxidation rate of metal ions in the catholyte.

BACKGROUND OF THE INVENTION The present invention relates to a process of-electrolytically preparing chlorine from hydrochloric acid. More particularly, the invention is directed to the formation of small oxygen containing bubbles in the catholyte so as to increase the oxidation rate of the metal ion product of this process. Ain'example of sucha process is U.S. Pat. 3,486,994 wherein a non-ionic, non-foaming wetting agent is introduced into the electrolyte to speed the reoxidation step. The oxygen containing gas was introduced into the catholyte through a frit at the lower edge of the cathode. 9

The oxidation and chlorine recovery process described in US Pat. 2,666,024 and further reported in volume 46', No. 9, page 456 of ChemicalEngineering Progress employs agitation impellers with air blown therethrough into the oxidizing tank. While operable, the efiiciency of such a process suffers because of a lack of adequately small bubbles.

It is, therefore, a primary purpose of this invention to provide a process to reduce bubble size to afiord a greater rate of oxidation of the metal ion in electrolytic chlorine producing equipment.

An additional object is to provide a method of im-,, proving the efficiency of the impeller bubble forming means in the oxidation step for electrolytically producing chlorine.

Other objects and advantages will become apparent during the course of the following description of the invention.

.THE INVENTION The above and other objects and advantages are found in the current invention, which is in a process comprising electrolyzing hydrochloric acid in a diaphragm cell having an anolyte and a catholyte to produce chlorine, the improvement which comprises adding a substantially nonfoaming, water-soluble, ionic, organic bubble size controlling agent to a catholyte; introducing an oxygen containing gas into said catholyte; and dispersing said gas to form small bubbles.

In the operation of this embodiment small oxygen containing bubbles. are formed in catholyte to which sufiicient bubble size controlling agent has been added to reduce the bubble size without excessive foaming. The small oxygen containing bubbles reoxidize metal chloride within the catholyte to a higher valence state. In this embodiment the catholyte can be reoxidized 'eithe'r internally or externally to the cathode'compa'rtment.

Gas dispersing means, such as a porous diffuser, spinnerette, impeller, or other turbine type gas dispersing mechanism, produce a smaller sized bubble when used in combination with anionic, organic bubble size curtailing additive than without the additive. The impeller or turbine type gas dispersing mechanism are preferred, since they do not clog as readily as other means of generating bubbles. The reduction in bubble size will afford an increase in interfacial area and a consequent increase in the oxidation rate of the metal ion contained in the catholyte. This increase in oxidation or mass-transfer rate will be proportional to the decrease in bubble size. The benefits of this invention willalso be realized in lower power consumption by the impeller in the oxidizer and an overall greater efiiciency of this electrolytic process. Y PREFERRED EMBODIMENT In the aforementioned process, a preferred organic bubble size controller is characterized in that a quantity of about 10' grams of the substance reduces the surface tension of about one liter of aqueous liquid to aminimum of about 30 dynes per centimeter at 25 C. While a reduction in surface tensionis desired, the organic additive must be substantially non-foaming in aqueous solutions. A substantially non-foaming agent is herein defined as one having foam stability factor not in excess of about 5%, where:

Percent foam stability:

The foam stability test as described in ASTM Standard Dl173-53 (1965) using distilled water was adhered to except that the testing temperature was room temperature or 25 C.

The amount of bubble size cont rolling agent must be sufficient to reduce the gas bubble size produced by the dispersing means without causing foaming in excess of that represented by a foam stability factor of 5%. This quantity is usually less than about 1% of the total weight.

Acids, or salts thereof, having at least one COOH group; such as, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, and halogenated derivatives thereof are useful bubble size controlling agents. Prior to use of any specific compound, the before mentioned foam test can be used to determine the foaming characteristics of the compound.

To avoid volatilization and resultant loss of the bubble size controlling additive, it is desirable but not mandatory that the bubble size controlling additive have a boiling point greater than about that of water.

Examples l-10 The following are exemplary of the surface tension and low foaming characteristics in an aqueous liquid of ionic,

organic bubble size controllingagents employable in this process.

TABLE I Foam stability in distilled water at 25 C., Concen- Surface foam height (mm.)

tration tension (gmJliter ar 25 C. After Compound of Water) (dynes/cm.) Initial mm 1 Property for this concentration was not determined,

Examples 11-16 The hereinafter named bubble size controlling agents were added to and mixed with aqueous solutions contained in laboratory type beakers. Each solution was agitating with an impeller, operating at 1,000 rotations per minute, concurrently with the introduction of a stream TABLE II Concen- Air tration flow Reduced (g'ram/ liters/ Y bubble Compound added to aqueous solutions liter) minute) size Acetic acid 1. 20 4. 98 Yes. Hexanoic acid 0. 53 4.98 Yes. 1.06 4.98 Yes. Chloroacetlc 8.0ld 1. 14 4. 98 Yes.

0 1. 14 23. 69 Yes.

What is claimed is: I

1.'In a process comprising electrolyzing hydrochloric acid in a diaphragmcell having an anolyte and a catholyte toproduce chlorine, the improvement which comprises adding a substantially non-foaming, water-soluble, ionic organic bubble size controlling agent selected from the group consisting of acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid and halogenated derivatives thereof to a catholyte, introducing an oxygen containing gas into said catholyte, and dispersing said gas to form small bubbles.

2. The process as recited in claim 1 wherein adding about 10 grams of said organic agent reduces the surface tension of the catholyte to a minimum of dynes per centimiter and is substantially non-foaming.

3. The process as recited in claim 2. wherein the adding step is carried out with an organic agent having a boiling point greater than about thatof water.

4. The process as recited in claim 1 wherein the adding step is carriedv out by adding saidorganic agent in a quantity less than about 1 percent by total weight and sufiicient to reduce bubble size.

5. The process as recited in claim 1 wherein an acid selected from the group consisting of acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, and octanoic acid is added to said catholyte.

6. The process as recited in claim 1 wherein acetic acid is added to said catholyte.

7. The process as recitedin claim 1 wherein dispersing said gas is accomplished with an impeller.

8. The process as recited in claim 1 wherein said organic agent is added in a quantity suflicient to reduce the bubble size'and up to'about 10 grams per liter of solution.

9. The process as recited in claim 5 wherein said organic agent is added in a quantity sufiicient to reduce the bubble size and up to about 10 grams per liter of solution.

10. The process as recited in claim 5 wherein the adding step is carried out by adding said organic agent in a quantity less than about 1 percent by total Weight and suflicient to reduce bubble size.

I References Cited UNITED STATES PATENTS 3,486,994 12/1969 Donges et al. 204-128 OTHER REFERENCES The Elfectof Organic Substances on the Transfer of 0 from Air Bubbles in H 0, by Eckantelder et al. A.I. Ch.E. J., vol. 7, No. 4, December 1961, pp. 631-634.

JOHN H. MACK, Primary Examiner R. L. ANDREWS, Assistant Examiner 

